A typical water-cooled internal combustion engine includes a cooling system that continuously circulates a coolant through the engine in order to dissipate heat generated by the combustion process and by friction. Without such a cooling system, the engine would experience thermal expansion of its moving parts until the engine seized.
In order for the cooling system to function properly, heat carried away from the engine by the coolant must be dissipated to the environment. This is typically done by circulating the heated coolant through a radiator and causing air to flow over the radiator's surface. During periods of elevated coolant temperature, the airflow caused by any motion of the vehicle is augmented by the operation of an engine coolant fan, which forces an increased amount of air to be drawn over the radiator surface.
Because the engine coolant fan is powered by the engine, operation of the coolant fan is a power drain upon the engine. Consequently, any fueling provided to the engine must be increased when the coolant fan is operational in order to maintain the same vehicle speed. Operation of the coolant fan therefore reduces the engine's fuel economy.
There is therefore a need for a method for controlling an engine coolant fan such that any adverse impact on the vehicle's fuel economy is minimized. The present invention is directed toward meeting this need.